1. Field of the Invention
The invention relates generally to the manufacturing processes and structures of semiconductor power devices. More particularly, this invention relates to simplified manufacturing processes and structural configurations of improved high voltage (HV) metal oxide semiconductor field effect transistors (MOSFET).
2. Description of the Prior Art
Conventional methods of manufacturing high voltage (HV) MOSFET devices are encountered with difficulties and limitations to further improve the performances due to different tradeoffs. In the vertical semiconductor power devices, there is a tradeoff between the drain to source resistance, i.e., on-state resistance, commonly represented by RdsA, i.e., Rds×Active Area, as a performance characteristic, and the breakdown voltage sustainable of the power device. Several device configurations have been explored in order to resolve the difficulties and limitations caused by these performance tradeoffs. Special P-composition (PCOM) structures are developed particularly to achieve these purposes. Specifically, the high voltage (HV) MOSFET devices implemented with the PCOM configurations include P-type dopant regions surrounding the sidewalls of the shielding trenches to link between the P-type body region formed at the top surface of the semiconductor substrate and a P-type dopant region below the shielding trenches. In order to form the sidewall dopant regions surrounding the trench sidewalls, the conventional methods apply an additional implanting mask with implanting openings to carry out the implantation processes on the trench sidewalls at the selected locations of the shielding trenches. Furthermore, in order to assure the dopant ions are implanted into the bottom portions of the trench sidewalls, implantations of dopant ions at high energy must be applied. The requirements of additional mask and the processes of applying high energy dopant ions cause the increase of the manufacturing costs. Additionally, high energy implantations into the bottom portions of the trench sidewalls followed with a diffusion process generally have less control of the formation of the dopant regions. These uncertainties of the manufacturing processes result in greater variations of device performance and less accurate control of the manufacturing qualities.
FIG. 1A is a top view of an implanting mask 100 used in the conventional process and FIGS. 1B and 1C are two cross sectional views illustrating the configurations of a high voltage (HV) MOSFET device formed by applying conventional process along lines 1-1′ and 2-2′ of FIG. 1A correspondingly. As shown in FIG. 1A, the implanting openings 11 are located on the selected regions of the trenches 12. In order to form a MOSFET device that can sustain high power operations, a PCOM (P-composition) configuration is formed. In this PCOM MOSFET structure, special dopant regions are formed in part of the areas 16 below the P-type body region 13 through the implanting openings 11 to link the P-type body region and a P-type dopant region 15 below the trench 12 as shown in FIG. 1C. Meanwhile, in other areas, the implantation forming the dopant regions below the body regions is blocked by the implanting mask 100. The implant mask shown in FIG. 1A blocks the dopant implanted through the sidewalls of the trench in areas around 1-1′. FIG. 1B shows a configuration where there are no dopant regions surrounding the trench sidewalls to link the body regions and the dopant regions below the trench bottom. As shown in FIGS. 1B-1C, the high voltage (HV) MOSFET device also includes a planar gate 17 formed atop the semiconductor substrate and a source 18 and a P++ contact 19 formed at a top portion of the P-type body region 13.
The conventional manufacturing processes as shown in FIGS. 1A to 1C requires an additional implanting mask. Furthermore, a high energy implant of P-type dopant, e.g., P-type dopant implant in the Mev ranges, is required to form the dopant regions below the body regions surrounding the trench sidewalls shown in FIG. 1C. The manufacturing costs are increased due to the additional Mask and high energy implant requirements.
Therefore, a need still exists for the ordinary skill in the art to improve the methods of manufacturing of the power devices, particularly the devices with the PCOM configuration to resolve these technical limitations. It is the purpose of this invention to provide new and improved methods of manufacturing and device configurations to eliminate the requirements of additional implanting mask and high energy implantations such that the above-discussed difficulties and limitations can be overcome.